MATLAB: Does cftool gives incorrect result(and different each time) with custom function? (nonlinear least squares method)

bessel functioncftoolcurve fittingcustom equationgamma functionnonlinear least squares

I try to fit my result using cftool with nonlinear least squares method and custom function.
My custom function has defined functions in Matlab, such like besselk and gamma.
It shows similar trend but it is not correct in theoretically.
Plus, additional problem what I have is that the different fitting results are generated each time.
What is the reason of this problem?
Is there any suggenstion to make reliable fiiting results?

Best Answer

https://www.mathworks.com/help/curvefit/fit.html#bto2vuv-1-StartPoint
"If no start points (the default value of an empty vector) are passed to the fit function, starting points for some library models are determined heuristically. For rational and Weibull models, and all custom nonlinear models, the toolbox selects default initial values for coefficients uniformly at random from the interval (0,1). As a result, multiple fits using the same data and model might lead to different fitted coefficients"
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